1. Field of Invention
The present invention relates to plasma excitation of optical emission spectroscopy samples and, more particularly, is directed towards radio frequency power oscillators for plasma excitation of such samples.
2. Description of the Prior Art
Recent developments in high temperature technology have resulted in application of such technology to spectroscopic systems as typified in U.S. Pat. No. 3,467,471. In such systems, a plasma of annular form is produced by passing a gas stream along the axis of an induction coil of a radio frequency power source comprising frequency determiners such crystal resonators and LC circuits, the induction coil being part of a tuned LC circuits. A sample to be analyzed is introduced into the plasma, whereby the sample atoms are excited and radiate characteristics radiation which is detected and measured. Such systems have suffered from the disadvantages of limited practicality and utility in that the introduction of the sample into the plasma changes the impedance of the induction coil which results in a detuning of the circuit and a decrease in the power transferred to the plasma. The reduction in the power transferred to the plasma results in loss of the plasma or faulty analytical measurements. In order to overcome the problem of reduced power transfer due to detuning, the LC circuit is retuned manually. This retuning procedure is a time consuming operation which is generally unacceptable in a high volume production system.